1. Field of the Invention
This invention relates to a flame retardant silicone composition which cures into a transparent product and is suitable for the protection of ICs and hybrid ICs.
2. Prior Art
For addition curing type silicone rubber compositions which cure into elastomers, a number of techniques are known for rendering them flame retardant. The most basic technique is to add platinum compounds to organopolysiloxanes. The addition of benzotriazoles, hydrazines and similar compounds is known effective for improving flame retardancy. Fumed titanium oxide, cerium oxide, cerium hydroxide, iron oxide and carbon powder are also known effective.
All the prior art silicone rubber compositions of this type contain reinforcing inorganic fillers such as fumed silica and quartz powder. Flame retardant silicone compositions essentially free from reinforcing inorganic fillers are unknown.
One known transparent material based on organopolysiloxane is silicone gel which finds use as a filler for parts used in optical equipment, a protective material for hybrid ICs used in electric and electronic parts to be mounted on automobiles, and a protective sealing agent for commercial power modules.
Although flame retardancy is essentially required in these fields, prior art silicone compositions could not meet the requirement. It was a common approach in the art to ensure that parts as a whole are flame retardant. As greater attention is now paid to the environmental problem, the requirement for flame retardancy becomes severe. There is a need for a silicone composition which offers not only transparency, but also flame retardancy.